Almost 100 years ago the excruciating pain of dental extraction, drilling and reconstruction was eliminated by the invention of local anesthetics. Ever since, however, one smaller but often agonizing pain has remained; ironically, it is the pain of the hypodermic injection itself. All practical attempts to eliminate it have failed.
While narrow gauge, sharp hypodermic needles can be inserted into the soft fleshy tissues of say an upper arm essentially without pain, save possible psychological pain, the pain of a hollow needle inserted into the hard, relatively inelastic gum and mouth tissues to engage the bone which carries the nerves to the teeth, is more often than not real. It is also complex. Pain can be felt when the needle first punctures the firm tissue and thereafter as the needle tip cuts through the tissue. Not infrequently the pain is amplified as the moving needle cuts out a tiny core of tissue which enters the bore in the hollow needle. Pain can be felt if the needle scrapes the bone membrane and even greater pain can be felt if the injected liquid mass distends and tears the tissue, particularly the interior tissue, away from the bone in one of the most sensitive portions of the body, before absorption and numbing occur. And pain can be felt if either the dentist or the patient or both are not steady, causing traumatic lateral displacement of the embedded needle.
The present state of the art in hypodermic anesthetic injections, particularly dental injections, is at best a hit or miss art reflecting the skill and luck of the operator rather than being a scientifically repeatable procedure. The tools are clumsy and ill-suited to their task, making the administration of local anesthetics in dentistry one of the less pleasant procedures for both the dentist and the patient alike.
The present invention has for its object to eliminate pain in all phases of and for all types of hypodermic anesthetic injection including four in dentistry considered most difficult and painful: the palatal, the mandibular, the interligamentary, and the maxillary anterior.
Another object of the invention is to provide a factory-sterilized, assembled and sealed hypodermic syringe sub-assembly to provide an unbroken chain of sterility from manufacturer to patient.
Another object of the invention is to provide a universal hypodermic syringe which can be used for all known dental injection procedures, which is pleasant and easy to use and which affords the dentist extraordinarily acute tactile response characteristics essential to good dentistry.
Another object of the invention is to provide a local anesthetic injection apparatus and method which reduces the amount of anesthetic required to perform dental procedures.
Still another object of the invention is to provide an aspirating hypodermic syringe using expendable pre-filled vials in which the reliability of the aspirating test cycle is assured.